The invention relates to an examination apparatus with a mass balancing device for a part of the apparatus which is pivotable about an axis. The mass balancing device comprises a compressed air cylinder which supports the pivotable apparatus part and in which a piston rod is slidably arranged. The compressed air cylinder comprises an opening for the inlet and outlet of air, and its internal pressure is controllable by means of a sine generator which generates a signal which corresponds to the sine of the pivot angle.
A device of this kind is known from U.K. patent application 2,014,667 (corresponding to German Auslegeschrift 2,806,956). This known device is also used for displacing the apparatus part, and its compressed air cylinder is divided into two chambers with different pressures. Each chamber comprises an opening through which air can be admitted or discharged, so that the apparatus part can be displaced in different directions. The required pneumatic control device is very complex and expensive. Once the compressed air source to which the compressed air cylinder is connected becomes defective, the apparatus part can no longer be displaced.
Furthermore, from U.S. Pat. No. 4,233,516 (corresponding to German Auslegeschrift 2,557,810) a stand is known for an X-ray image forming device in which a displaceable apparatus part is supported by a gas-pressure operated spring. Even though mass balancing in this device is substantially simpler than in the previously described device, the apparatus part can be displaced only in the vertical direction.